Numerical investigation of Vortex-Induced Vibrations (VIV) of an elastically-mounted circular cylinder beneath a Free Surface: Modes & Frequencies

In this paper, a two-dimensional numerical simulation is applied to study the Vortex-Induced Vibrations (VIV) of an elastically mounted rigid circular cylinder beneath a free surface of fluid. The effect of free surface in laminar flow (60 < Re < 130) with Fr=0.2 is investigated with considering two Gap-Ratios of 2.5, 1.5. The natural structural frequency of oscillator is assumed to match the vortex shedding frequency for a stationary cylinder at Re=100. Discretization of flow equations based on the Finite Volume method was implemented in CFD commercial software Ansys Fluent 14.0. Simulations of VIV and Free Surface of fluid flow have separately shown good agreement with previous results. This paper is the second part of an investigation about effects of Free Surface of fluid on VIV phenomena. The effects of Free Surface is investigated with using a comparison of vortex shedding modes and non-dimensional frequency diagrams for the two gap-ratios. With approaching cylinder to free surface, results shows changing type of vortex shedding modes, abatement in lock-in region, increasing Strouhal number and non-dimensional frequency ratio.